Most girder bridges are designed from two main girders which function as static bending beams. In this respect, the roadway surface runs over the supporting structure and therefore functions as a cover for the supporting structure at the same time. Since the main girders are thus protected under the road surface, the system provides the best requirements for an optimum structural timber protection with limited maintenance costs.
Girder bridges offer a good cost-benefit balance with a visually appealing appearance. They are frequently used as single span bridges.
Structural timber protection is the key to the longevity of a timber bridge. Structural timber protection intends for all structural timber components to be completely protected. In this respect, the following steps are taken into consideration: Installation of technically dried timber with a timber humidity of 12% in order to prevent insect infestation, protection against weathering, ingress of moisture, UV rays due to the installation of projections and skirting in the design as well as good air circulation to encourage drying out. Constructions designed in this way satisfy the requirements of protected timber bridges pursuant to DIN EN 1995-2 NA. This means that loss events are prevented and maintenance costs are minimised, and the use of timber preserving chemicals can be reduced and/or avoided. Structures protected according to DIN EN 1995-2 have a service life of 60 - 80 years*.
* Source: Redemption amounts calculation regulations - ABBV, BMVBS, status 2010 and study of DGfH 2006
Here is a selection of laminated timber girder bridges.